I occassionally have problems with Thunderbird sending emails. I will get the progress bar for sending mail, but it takes several seconds to get past the start, or it stays up for a while after the bar shows 100%. In my case, it seems to be an issue of the SMTP server being temporarily overloaded. Several of my email accounts are hosted with Google apps, and I see this happen with those accounts more often. I don't believe there is anything wrong, just that the mail servers sometimes get busy. If I cancel and send the email again, it usually goes much faster. I usually don't see this any more than say once a week or less. I am not sure if that is your situation.

The other thing I have noticed is if the accounts are not configured properly, Thunderbird seems to wait a long time trying to set up the connection. So you might check the configurations. especially the password and type of security used in the authentication. On a few occassions Thunderbird has seemed to lose my stored password. It will take a long time to respond, then give me a text entry box asking for the password. If I reenter the correct password for the mail account, it has always worked. That is very rare.

In TB 10.0.2, I still have the option for replying in the same place. Under Account Settings > Name of email > Composition and Addressing. Click check box to "automatically quote the original message when replying. Then select "start my reply above the quote" or whichever option you want.